Means for producing a plaster or like cast



Aug. 9, 1960 G. s. CHASE MEANS FOR PRODUCING A PLASTER OR LIKE CAST Filed July 16, 19s? 3 Sheets-Sheet 1 Fla.

1950 a. s. CHASE 2,948,017

MEANS FOR PRODUCING A PLASTER OR LIKE CAST Filed July 16, 1957 s Sheets-Sheet 2 Fla 5 23 22 a k i! 9, 1950 e. s. CHASE 2,948,017

MEANS FOR PRODUCING A PLASTER 0R LIKE cAs'r Filed July 16, 1957 5 Sheets-Sheet a JE a 7% Unite ff 3 Claims. (CI. 18-57) The invention relates to a means of producing a plaster or like cast, and is of particular application in dentistry in the production of'artificial teeth.

A preliminary operation in the production of artificial teeth involves taking an impression of the patients teeth or gums in a mouldable substance such as a thermoplastic resin which is held on a tray of various shapes and forms. Plaster of Paris in liquid form is poured into this impression after which a period of time must be allowed to lapse while the plaster partially sets. A further amount of partially set plaster is then poured or spatulated onto a surface and the impression containing the first amount of plaster is then inverted onto this second mass or mound of plaster and the sides are spatulated upwards to join the two masses of plaster together to form the plaster model or cast. When the plaster has set the tray and impression material are removed from the model or cast and further trimming of the model is then necessary to bring it to a suitable size and shape for further use. This ordinary method of casting an impression requires the continuous presence of the operator to avoid the danger of the plaster setting too quickly. Furthermore, for the same reason it is not prudent to cast more than four impressions at the same time. 7

If an artificial stone plaster is to be used the method hereinbefore described cannot safely be employed as the setting time of such plaster is considerably longer than that of normal, superfine dental plaster of Paris and artificial stone is pulled away by gravity whilst still in the liquid state from the surface of the inverted impression, thus giving an inaccurate model. Furthermore, the weight of the tray and impression is likely to cause sinking of the tray and impression into the artificial stone before this has set sufliciently .to withstand the force of gravity, causing the stone to spread sideways and resulting in a model of insuiiicient thickness. The usual method of overcoming this difficulty with artificial stone is to box the impression. To box an impression, a wall of thin wax sheet or soft metal foil or paper or cardboard is, moulded by hand completely around the impression and tray. The junctions of the sheet or sheets and the junction of sheet and impression are then sealed with molten wax or plasticene or clay to form a water-tight container around the impression, into which the plaster or artificial stone is poured so as to cover the impression to a sulficient thickness to form a suitable model or cast. The poured material is then allowed to set with the impression and tray continually in the upright position,. the wax,.metal foil or the like being then removed. This operation of boxing is timeconsuming andrequires great care in order that'the wax States Patent or other relatively hard substance used shall not damage the impression. Furthermore, the wax sheeting can only be used once or twice before it breaks up.

q Theinventi'on has among its objects to avoid the disadvantagesof known methods of boxing in waste of material and consumption of time by providing simple, quick and inexpensive means for boxing all impressions in situ in the tray and which means may be used repeatedly, rapidly and in simple manner thus allowing many more than four impressions to be cast with one mix of plaster of Paris. It is a further object of the invention to avoid the disadvantage of known methods of boxing when artificial stone must be used.

According to the invention the impression mounted on a tray is placed in a container comprising essentially a base and a containing wall, which is made of a flexible material in such manner as to be adapted to be readily applied around trays of varying dimensions to assume a static form so as to provide a cup-shaped container to receive the plaster or the like without danger of the material of the container in any way damaging the impression by contact therewith, and so as to be adapted to be readily removed when the plaster is set, for immediate use if desired, in subsequent boxing operations.

' The means for forming the container may be made of a resilient or flexible material, such as rubber, a suitable synthetic material, for example, polyethylene, paper, waximpregnated paper or card.

When the container is made of paper, Waxed paper or card the initial cost of the article would, when produced on a large scale, be so small as to permit a fresh container to be economically used for each boxing or casting operation.

In one construction according to the invention, the container is formed from a flexible sheet of rubber or foam rubber backed with a textile material, such as linen or canvas, by a cutting or stamping operation. The flexibl e sheet of rubber is so cut and stamped to provide a unit comprising a base, and parts integral with the base which are adapted to be readily flexed around an impression placed on the base to form walls of the container into which the plaster may be poured.

The flexible members forming the walls of the container may be. retained in their position by any suitable means, for example, a clip. Alternatively, one or more pressstuds or. other snap-connecting means may be provided on the flexible members.

In a further construction according to the invention, the container is formed of foam rubber by a moulding operation and comprises a base member having an upstanding back member, each end of the upstanding back member being extended to form a wing, the wings being adapted to be flexed to enfold an impression placed on the base member and thereby to form the walls of the container. The base member may be provided' with means, such as ribs and/or lips, on its surface in which wings are adapted to engage when in the position of use. A slot may be provided at the bottom of the upstanding member through which the handle of the tray carrying the impression may extend. r

The flexible members and/or other parts of the container may be reinforced, for example, by metal inserts in the form of strip or wire. Such metal inserts may be resilient and may be adapted to urge the flexible members 'into the open position or to urge the flexible members into the positions in which they form the walls of the container to receive the plaster or the like in the boxing operation. Alternatively the inserts may be nonresilient so as to tend to maintain the flexible members in positions in which they are placed by hand.

Flap portions which project so as to be adapted to be bent over other parts may be provided on the flexible members and/or base so that a container is formed which retains the shape when once it has been bent around the impression and tray. Q a a 1 When the impression being boxed is that of the lower jaw, a hung or plug is advantageously provided iniithe container between the two limbs of the impression,

Such a bung or plug may be provided integral with the base part of the container.

The invention is diagrammatically illustrated by way of example in theaccompanying drawings, in which:

' Figure 1 is a plan of one construction;

Figure 2 is a rear elevation of the construction shown in the Figure l Figure 3- is a section on the line A- A of Figurel; Figure 4 is a section on the line B-B of Figure 1;

Figure 5 is a plan of a further construction;

Figure 6 is a section on the line X-X of Figure 5, and

Figure 7 is a plan of another construction;

Figure 8 is a plan view of a further modification of V the invention; and

Figure 9 is a section on the line ZZ of Figure 8. The construction illustrated in Figures 1 to 4 comprises a. base part 1 provided with an upstanding back member 2 the ends of which are extended to form wings 3, the whole being made of foam rubber and formed as a unit by a moulding operation.

The base part 1 is provided with a pair of symmetrically disposed upstanding lips '4 which extend from a position adjacent to the back member 2 to the front of the base part 1. The lips 4 decrease in height towards the back member 2 and merge at their forward ends into an intermediate ridge 5 of a height lower than that of the adjacent parts of the lips 4. Pairs of arcuate ribs 6 are symmetrically disposed on the upper surface of the base part 1. V

The thickness of the wings 3 tapers towards their outer ends and the lower, outer edge of each wing 3, at a position adjacent to the outer or free end of the wing, is flared outwardly at 8.

In use the tray carrying the dental impression is placed on the base part 1 with the back of the tray or impression in contact with or adjacent to the back member 2 and with the handle of the tray resting on the ridge 5. The wings 3 are then bent inwardly to encircle and box the tray and the impression, the overlapping ends of the wings 3 being secured together as by means of a clip or other suitable means. Each of the wings -3 engages with its flared, lower edge 8 in one of the ribs 6 or with a lip 4, and the wings 3 and the back member 2 thus form the walls of a box or container into which the plaster or other substances may be poured to take a cast of the dental impression carried by the tray.

The construction illustrated in Figures 5 and 6 consists of a unit moulded from foamed rubber and comprises a base part 10 and a wall 11 provided at its ends with wings 12, the wings 12 advantageously tapering in thickness towards their free ends. A hole or slot 13 is provided at the base of the wall 11 at a mid-position of its length. In use, the tray carrying the dental impression is placed on the base part 10 with the handle of the tray extending through the slot 13. The portion of the base part 10 adjacent to the free ends of the wings 12 is bent upwardly to lie against the rear end of the tray and the wings 12 are flexed inwardly about the upstanding portion of the base part 10 with one wing 12 overlapping the other wing 12. The upstanding portion of the base part 10 and the overlapping ends of the wings 12 are clipped or otherwise secured together to form the wall of the box into which the plaster or other casting material may be poured.

The construction illustrated in Figure 7 comprises a flexible layer of foamed rubber backed by linen formed by a cutting or stamping operation. from a sheet of the material or othersuitable material and comprises a front member 20 and a back member 21.

t The back member 21 is secured to the front member 20 by an intermediate portion 22 in which is provided a hole or slot 23. The back portion 21 is provided at its rearward end with two parallel cuts or slots 24 to divide the back part 21 into a pair of outer wings 25 and a central member 26. In use the tray carrying the dental impression is placed on the back part 21 with the handle of the tray extending through the slot 23.

The ends of the front member 20 are wrapped around the impression, thus flexing about the portion 22 to form an upstanding wall encircling the tray and impression. The central member 26 is then bent upwardly into contact with the upstanding ends of the member 20 at the back .of the tray, after which the wings 25 are raised two outer ends of the front member 20. The outer ends of the front member 20, the wings 25 and the central member 26 are then secured together in their upstanding position by means of .a clip or other suitable fastening means. In this manner a box or cup is formed into which the plaster can be poured for taking a cast of the dental impression.

Two inwardly directed slots 27 may be provided in the front member 21 at positions adjacent to the slot 23.

.In the modification illustrated in Figures 8 and 9 a plug or bung 28 is formed integral with the back member 2 and the base part 1. The bung 28 occupies the space formed by the tongue cavity. The bung 28 may be formed separately from the base part 1 and the back member 2, and may be adapted to be inserted into the tongue cavity when required.

The upper surface of the base part 1 may be formed with a cutaway portion 29 which is adapted to receive the handle of the impression tray thus ensuring that the impression tray rests on the base part 1 in a horizontal position.

No limitation is involved as to .the form which the container may take, or the material of which it may be made, provided only that members which are adapted to form part at least of the wall of the container are provided of a flexible material that is adapted readily to be bent to form a cup-shaped container around the impression and tray, and which can be readily opened out when the plaster is set for further use.

What I claim is:

1. A holder for the support of a dental impression tray, to receive a moulded impression over which a mouldable substance such as Plaster of Paris is poured, for the production of a cast of the impression, as in the manufacture of false teeth, comprising a unitary I flexible member having a base, the rearward portion of which extends upwardly as a wall and which further extends laterally beyond the base to form flexible, variably overlappable sidewall members which when overlapped laterally form, with said base, an open cup-shaped container and means for engaging and retaining the sidewalls in their overlapped position adjacent the upper surface of said base.

2. A holder according to claim 1, in which the base is provided on its upper surface with one or more pairs of symmetrical, arcuate ribs adapted to engage the lower edge of the sidewall members.

3. A holder according to claim 1, in which the flexible members and the base are reinforced with a metallic member or metallic members.

References Cited in the file of this patent UNITED STATES PATENTS 752,378 Dailey Feb. 16, 1904 1,599,487 Porter Sept. 14, 1926 1,701,619 Kendall -1 Feb. 12, 1929 1,834,980 Stealy Dec. 8, 1931 2,030,524 Lambert Feb. 1, 1936 2,139,631 Dresch et al. Dec. 6, 1938 2,187,260 Brandenburg Jan. 16, 1940 2,245,849 Ballard June 17, 1941 2,577,250 Kibber Dec. 4, 1951 2,735,154 Killian et al. Feb. 21, 1956 

